OP does not actually name any managed switches, only "Smart," mostly L2 ones that are in a different price range.
A switch is either managed or unmanaged. "Smart switches" are just a marketing term. Yes, there are varying degrees of management, and obviously an L3/L4 managed switch will have more features than an L2 managed switch.
One of OP's questions was if managed switches can improve performance and the simple answer is no--gigabit is gigabit at wire speed. The more thorough answer is that managed switches, particularly if using any complex software features, are actually slower than unmanaged switches in latency. For example the GS724T is rated at 20microseconds with everything disabled, which is the same as an unmanaged switch from 2003 (the latest v4 one claims 4.5microseconds). This minor performance loss is the cost for those useful management features, which help to troubleshoot, monitor and manipulate networks (hey, at least it's better now than 350microseconds, which is enough time for data to travel >50km over a wire).
None of this takes into account the ASIC's of various switches. Yes, you can do line speed on a single port on any gigabit switch, but how does the switch handle it when multiple ports are in use? That's the more important metric. Lower-end switches are often oversubscribed. And you have to make sure you look at the aggregate bandwidth because gigabit ports are gigabit in both directions simultaneously. So, having put all of that together, fully managed switches are usually faster than unmanaged switches when every port is pushed. In other words, don't skimp out on your core switches.
OP's other main question is if different switches may be more reliable in that environment. Well sure, build quality is all over the map. It may be that even another cheap switch like OP's mentioned D-Link would not have failed under the same circumstances, but nobody can really answer such a question with any certainty. My ancient Vitesse gigabit switches are still working after 14 years, and they are filled with terrible Jackcon caps that haven't failed yet.
This I agree with. There is no fixing dirty power. The best you can do is stick a decent UPS on it and hope it does what it's supposed to do.
The 1920's are good, and are clearly re-badged 3Com, but pretty solid.
Well, they're only rebadged in the sense that HP bought 3Com years ago.